Alteplase acts by -

Ans. is 'a' i.e., Converting plasminogen to plasmin Fibrinolytic drugs* These are drugs used to lyse thrombi/clot to recanalize occluded blood vessels. Normally fibrin clot is lysed by an enzyme plasmin (a serine protease) which is generated from plasminogen by tissue plasminogen activator (t-PA), which is produced by vascular endothelium.* Plasminogen circulates in plasma (free form) as well as remains bound to fibrin.* The t-PA selectively activates fibrin bound plasminogen within the thrombus, and any plasmin that leaks is inactivated by circulating antiplasmins.* Fibrin bound plasmin is not activated by antiplasmins because of common binding site for both fibrin and antiplasmin.* When excessive amounts of plasminogen are activated by administration of fibrinolytics, the a2 antiplasmin is exhausted and active plasmin persists in plasma - Lytic state.* Streptokinase is obtained from group 'c' b-hemolytic streptococci. It activates both circulating and fibrin bound plasminogen. It is antigenic, can cause allergic reactions. Urokinase is prepared from cultured human kidney cells. It is not antigenic. Alteplase, Reteplase and tenecteplase are recombinant t-PA. These are nonantigenic. They activate fibrin bound plasminogen only. Alteplase has very short half life of 5 min* Recombinant prourokinase and alteplase are termed fibrin selective, for they bind strongly to fibrin, and are capable of dissolving aging or lysis resistant thrombi better than nonfibrin-selective agents.